Subnanogram amounts of bromocriptine (BCT) were quantitated in patients samples using high-performance liquid chromatography (HPLC) method with electrochemical (EC) detection recently developed in this laboratory. The new method has a 10 fold improvement in sensitivity over exisitng methods and facilitates direct injection of plasma samples without organic extraction. With a limit of detection of 0.05 ng BCT/ml plasma, the HPLC method offers a unique opportunity for clinical pharmacokinetic studies of bromocriptine in prolactinoma and acromegaly patients who usually receive low doses of the drug (0.6 - 2.5 mg/day) and in whom such studies would be difficult. Preliminary data on this project including a retroactive study of plasma bromocriptine levels in six patients who received 0.6 - 10 mg doses of the drug were recently presented at a 41st Annual Meeting of ASHP.